1. Field of the Invention
The present invention relates to a method and apparatus for testing the quality of an optical disk medium and an optical disk medium; and more particularly, to such a method and apparatus having improved accuracy and reliability.
2. Description of Related Art
Disk media are divided into two groups, magnetic disks and optical disks such as compact disks (CDs). Because of their large storage capacity, the demand for optical disks has rapidly increased.
FIGS. 1A and 1B illustrate conventional optical disks. The radius L1 of these disks is 60 mm, while the diameter L2 of the center hole is 15 mm. FIG. 1A illustrates a conventional prerecorded optical disk. As shown in FIG. 1A, a recording area of the optical disk includes a lead-in start point BLI, a main storage area start point BPL, and a lead-out start point BLO. Information is written in the main storage area MSA between the main storage area start point BPL and lead-out start point BLO.
FIG. 1B illustrates a conventional write-once optical disk upon which no information has been recorded. As with the optical disk of FIG. 1A, the optical disk of FIG. 12 has a recording area, and when information is recorded thereon, this information is recorded in a main storage area MSA. As shown in both FIGS. 1A and 1B, an outer area of the recording area is not used to store information. This provides a margin of error with respect to manufacturing defects since defects in the recording area are much more likely to occur in the outer area of the recording area due to the manufacturing techniques used.
With magnetic and magneto-optic disks, conventional quality test methods involved recording signals in the lead-in area or main storage area of the disks, reproducing those test signals, and comparing the test signals to reference signals to determine quality;
These methods have been applied to the quality testing of optical disks. Unfortunately, however, these methods cannot be applied to every optical disk manufactured. For instance, once test data is written into a write-once optical disk, that disk loses its value as a commercial good because it becomes unusable. Accordingly, samples from a plurality of manufactured optical disks are taken and tested according to the above-described methodology.
Besides rendering the sampled disks unusable, these quality testing techniques also prove to be inaccurate and unreliable. Just because the sampled disks may be of sufficient quality does not necessarily mean that the other disks, not sampled, are of sufficiently high quality. Therefore, these tests tend to be inaccurate and unreliable.
These optical disk media also undergo additional quality tests. For instance, the entire surface of the optical disk is displayed by monitoring the scanning of the optical disk surface with a laser beam using a CCD camera. The surface is then visually checked using the display.
Other tests include push/pull, crosstalk, and checking the location of the lead-in start point BLI, main storage area start point BPL, and lead-out start point BLO.
Through the above described test process, mechanical characteristic measurements such as the lead-in start point BLI, the main storage area start point BPL, the lead-out start point BLO, a track and index start point, a test speed, a track pitch, a bow deflection, a warp deflection, a thickness of the optical disk, an angular deflection, a vertical deflection, the radius of the optical disk, and the diameter of the center hole of the optical disk are checked. In addition, signal characteristics such as radial noise, focal noise, push/pull of a tracking signal, data carrier analog, and carrier digital are checked.